<?php

/**
 * Interface for entity controller classes.
 *
 * All entity controller classes specified via the 'controller class' key
 * returned by hook_entity_info() or hook_entity_info_alter() have to implement
 * this interface.
 *
 * Most simple, SQL-based entity controllers will do better by extending
 * DrupalDefaultEntityController instead of implementing this interface
 * directly.
 */
interface DrupalEntityControllerInterface {

	/**
	 * Constructor.
	 *
	 * @param $entityType
	 *   The entity type for which the instance is created.
	 */
	public function __construct($entityType);

	/**
	 * Resets the internal, static entity cache.
	 *
	 * @param $ids
	 *   (optional) If specified, the cache is reset for the entities with the
	 *   given ids only.
	 */
	public function resetCache(array $ids = NULL);

	/**
	 * Loads one or more entities.
	 *
	 * @param $ids
	 *   An array of entity IDs, or FALSE to load all entities.
	 * @param $conditions
	 *   An array of conditions in the form 'field' => $value.
	 *
	 * @return
	 *   An array of entity objects indexed by their ids. When no results are
	 *   found, an empty array is returned.
	 */
	public function load($ids = array(), $conditions = array());
}

/**
 * Default implementation of DrupalEntityControllerInterface.
 *
 * This class can be used as-is by most simple entity types. Entity types
 * requiring special handling can extend the class.
 */
class DrupalDefaultEntityController implements DrupalEntityControllerInterface {

	/**
	 * Static cache of entities.
	 *
	 * @var array
	 */
	protected $entityCache;

	/**
	 * Entity type for this controller instance.
	 *
	 * @var string
	 */
	protected $entityType;

	/**
	 * Array of information about the entity.
	 *
	 * @var array
	 *
	 * @see entity_get_info()
	 */
	protected $entityInfo;

	/**
	 * Additional arguments to pass to hook_TYPE_load().
	 *
	 * Set before calling DrupalDefaultEntityController::attachLoad().
	 *
	 * @var array
	 */
	protected $hookLoadArguments;

	/**
	 * Name of the entity's ID field in the entity database table.
	 *
	 * @var string
	 */
	protected $idKey;

	/**
	 * Name of entity's revision database table field, if it supports revisions.
	 *
	 * Has the value FALSE if this entity does not use revisions.
	 *
	 * @var string
	 */
	protected $revisionKey;

	/**
	 * The table that stores revisions, if the entity supports revisions.
	 *
	 * @var string
	 */
	protected $revisionTable;

	/**
	 * Whether this entity type should use the static cache.
	 *
	 * Set by entity info.
	 *
	 * @var boolean
	 */
	protected $cache;

	/**
	 * Constructor: sets basic variables.
	 */
	public function __construct($entityType) {
		$this->entityType = $entityType;
		$this->entityInfo = entity_get_info($entityType);
		$this->entityCache = array();
		$this->hookLoadArguments = array();
		$this->idKey = $this->entityInfo['entity keys']['id'];

		// Check if the entity type supports revisions.
		if (!empty($this->entityInfo['entity keys']['revision'])) {
			$this->revisionKey = $this->entityInfo['entity keys']['revision'];
			$this->revisionTable = $this->entityInfo['revision table'];
		}
		else {
			$this->revisionKey = FALSE;
		}

		// Check if the entity type supports static caching of loaded entities.
		$this->cache = !empty($this->entityInfo['static cache']);
	}

	/**
	 * Implements DrupalEntityControllerInterface::resetCache().
	 */
	public function resetCache(array $ids = NULL) {
		if (isset($ids)) {
			foreach ($ids as $id) {
				unset($this->entityCache[$id]);
			}
		}
		else {
			$this->entityCache = array();
		}
	}

	/**
	 * Implements DrupalEntityControllerInterface::load().
	 */
	public function load($ids = array(), $conditions = array()) {
		$entities = array();

		// Revisions are not statically cached, and require a different query to
		// other conditions, so separate the revision id into its own variable.
		if ($this->revisionKey && isset($conditions[$this->revisionKey])) {
			$revision_id = $conditions[$this->revisionKey];
			unset($conditions[$this->revisionKey]);
		}
		else {
			$revision_id = FALSE;
		}

		// Create a new variable which is either a prepared version of the $ids
		// array for later comparison with the entity cache, or FALSE if no $ids
		// were passed. The $ids array is reduced as items are loaded from cache,
		// and we need to know if it's empty for this reason to avoid querying the
		// database when all requested entities are loaded from cache.
		$passed_ids = !empty($ids) ? array_flip($ids) : FALSE;
		// Try to load entities from the static cache, if the entity type supports
		// static caching.
		if ($this->cache && !$revision_id) {
			$entities += $this->cacheGet($ids, $conditions);
			// If any entities were loaded, remove them from the ids still to load.
			if ($passed_ids) {
				$ids = array_keys(array_diff_key($passed_ids, $entities));
			}
		}

		// Load any remaining entities from the database. This is the case if $ids
		// is set to FALSE (so we load all entities), if there are any ids left to
		// load, if loading a revision, or if $conditions was passed without $ids.
		if ($ids === FALSE || $ids || $revision_id || ($conditions && !$passed_ids)) {
			// Build the query.
			$query = $this->buildQuery($ids, $conditions, $revision_id);
			$queried_entities = $query
			->execute()
			->fetchAllAssoc($this->idKey);
		}

		// Pass all entities loaded from the database through $this->attachLoad(),
		// which attaches fields (if supported by the entity type) and calls the
		// entity type specific load callback, for example hook_node_load().
		if (!empty($queried_entities)) {
			$this->attachLoad($queried_entities, $revision_id);
			$entities += $queried_entities;
		}

		if ($this->cache) {
			// Add entities to the cache if we are not loading a revision.
			if (!empty($queried_entities) && !$revision_id) {
				$this->cacheSet($queried_entities);
			}
		}

		// Ensure that the returned array is ordered the same as the original
		// $ids array if this was passed in and remove any invalid ids.
		if ($passed_ids) {
			// Remove any invalid ids from the array.
			$passed_ids = array_intersect_key($passed_ids, $entities);
			foreach ($entities as $entity) {
				$passed_ids[$entity->{$this->idKey}] = $entity;
			}
			$entities = $passed_ids;
		}

		return $entities;
	}

	/**
	 * Builds the query to load the entity.
	 *
	 * This has full revision support. For entities requiring special queries,
	 * the class can be extended, and the default query can be constructed by
	 * calling parent::buildQuery(). This is usually necessary when the object
	 * being loaded needs to be augmented with additional data from another
	 * table, such as loading node type into comments or vocabulary machine name
	 * into terms, however it can also support $conditions on different tables.
	 * See CommentController::buildQuery() or TaxonomyTermController::buildQuery()
	 * for examples.
	 *
	 * @param $ids
	 *   An array of entity IDs, or FALSE to load all entities.
	 * @param $conditions
	 *   An array of conditions in the form 'field' => $value.
	 * @param $revision_id
	 *   The ID of the revision to load, or FALSE if this query is asking for the
	 *   most current revision(s).
	 *
	 * @return SelectQuery
	 *   A SelectQuery object for loading the entity.
	 */
	protected function buildQuery($ids, $conditions = array(), $revision_id = FALSE) {
		$query = db_select($this->entityInfo['base table'], 'base');

		$query->addTag($this->entityType . '_load_multiple');

		if ($revision_id) {
			$query->join($this->revisionTable, 'revision', "revision.{$this->idKey} = base.{$this->idKey} AND revision.{$this->revisionKey} = :revisionId", array(':revisionId' => $revision_id));
		}
		elseif ($this->revisionKey) {
			$query->join($this->revisionTable, 'revision', "revision.{$this->revisionKey} = base.{$this->revisionKey}");
		}

		// Add fields from the {entity} table.
		$entity_fields = $this->entityInfo['schema_fields_sql']['base table'];

		if ($this->revisionKey) {
			// Add all fields from the {entity_revision} table.
			$entity_revision_fields = drupal_map_assoc($this->entityInfo['schema_fields_sql']['revision table']);
			// The id field is provided by entity, so remove it.
			unset($entity_revision_fields[$this->idKey]);

			// Remove all fields from the base table that are also fields by the same
			// name in the revision table.
			$entity_field_keys = array_flip($entity_fields);
			foreach ($entity_revision_fields as $key => $name) {
				if (isset($entity_field_keys[$name])) {
					unset($entity_fields[$entity_field_keys[$name]]);
				}
			}
			$query->fields('revision', $entity_revision_fields);
		}

		$query->fields('base', $entity_fields);

		if ($ids) {
			$query->condition("base.{$this->idKey}", $ids, 'IN');
		}
		if ($conditions) {
			foreach ($conditions as $field => $value) {
				$query->condition('base.' . $field, $value);
			}
		}
		return $query;
	}

	/**
	 * Attaches data to entities upon loading.
	 * This will attach fields, if the entity is fieldable. It calls
	 * hook_entity_load() for modules which need to add data to all entities.
	 * It also calls hook_TYPE_load() on the loaded entities. For example
	 * hook_node_load() or hook_user_load(). If your hook_TYPE_load()
	 * expects special parameters apart from the queried entities, you can set
	 * $this->hookLoadArguments prior to calling the method.
	 * See NodeController::attachLoad() for an example.
	 *
	 * @param $queried_entities
	 *   Associative array of query results, keyed on the entity ID.
	 * @param $revision_id
	 *   ID of the revision that was loaded, or FALSE if the most current revision
	 *   was loaded.
	 */
	protected function attachLoad(&$queried_entities, $revision_id = FALSE) {
		// Attach fields.
		if ($this->entityInfo['fieldable']) {
			if ($revision_id) {
				field_attach_load_revision($this->entityType, $queried_entities);
			}
			else {
				field_attach_load($this->entityType, $queried_entities);
			}
		}

		// Call hook_entity_load().
		foreach (module_implements('entity_load') as $module) {
			$function = $module . '_entity_load';
			$function($queried_entities, $this->entityType);
		}
		// Call hook_TYPE_load(). The first argument for hook_TYPE_load() are
		// always the queried entities, followed by additional arguments set in
		// $this->hookLoadArguments.
		$args = array_merge(array($queried_entities), $this->hookLoadArguments);
		foreach (module_implements($this->entityInfo['load hook']) as $module) {
			call_user_func_array($module . '_' . $this->entityInfo['load hook'], $args);
		}
	}

	/**
	 * Gets entities from the static cache.
	 *
	 * @param $ids
	 *   If not empty, return entities that match these IDs.
	 * @param $conditions
	 *   If set, return entities that match all of these conditions.
	 *
	 * @return
	 *   Array of entities from the entity cache.
	 */
	protected function cacheGet($ids, $conditions = array()) {
		$entities = array();
		// Load any available entities from the internal cache.
		if (!empty($this->entityCache)) {
			if ($ids) {
				$entities += array_intersect_key($this->entityCache, array_flip($ids));
			}
			// If loading entities only by conditions, fetch all available entities
			// from the cache. Entities which don't match are removed later.
			elseif ($conditions) {
				$entities = $this->entityCache;
			}
		}

		// Exclude any entities loaded from cache if they don't match $conditions.
		// This ensures the same behavior whether loading from memory or database.
		if ($conditions) {
			foreach ($entities as $entity) {
				$entity_values = (array) $entity;
				if (array_diff_assoc($conditions, $entity_values)) {
					unset($entities[$entity->{$this->idKey}]);
				}
			}
		}
		return $entities;
	}

	/**
	 * Stores entities in the static entity cache.
	 *
	 * @param $entities
	 *   Entities to store in the cache.
	 */
	protected function cacheSet($entities) {
		$this->entityCache += $entities;
	}
}

/**
 * Exception thrown by EntityFieldQuery() on unsupported query syntax.
 *
 * Some storage modules might not support the full range of the syntax for
 * conditions, and will raise an EntityFieldQueryException when an unsupported
 * condition was specified.
 */
class EntityFieldQueryException extends Exception {}

/**
 * Retrieves entities matching a given set of conditions.
 *
 * This class allows finding entities based on entity properties (for example,
 * node->changed), field values, and generic entity meta data (bundle,
 * entity type, entity id, and revision ID). It is not possible to query across
 * multiple entity types. For example, there is no facility to find published
 * nodes written by users created in the last hour, as this would require
 * querying both node->status and user->created.
 *
 * Normally we would not want to have public properties on the object, as that
 * allows the object's state to become inconsistent too easily. However, this
 * class's standard use case involves primarily code that does need to have
 * direct access to the collected properties in order to handle alternate
 * execution routines. We therefore use public properties for simplicity. Note
 * that code that is simply creating and running a field query should still use
 * the appropriate methods to add conditions on the query.
 *
 * Storage engines are not required to support every type of query. By default,
 * an EntityFieldQueryException will be raised if an unsupported condition is
 * specified or if the query has field conditions or sorts that are stored in
 * different field storage engines. However, this logic can be overridden in
 * hook_entity_query().
 *
 * Also note that this query does not automatically respect entity access
 * restrictions. Node access control is performed by the SQL storage engine but
 * other storage engines might not do this.
 */
class EntityFieldQuery {
	/**
	 * Indicates that both deleted and non-deleted fields should be returned.
	 *
	 * @see EntityFieldQuery::deleted()
	 */
	const RETURN_ALL = NULL;

	/**
	 * TRUE if the query has already been altered, FALSE if it hasn't.
	 *
	 * Used in alter hooks to check for cloned queries that have already been
	 * altered prior to the clone (for example, the pager count query).
	 *
	 * @var boolean
	 */
	public $altered = FALSE;

	/**
	 * Associative array of entity-generic metadata conditions.
	 *
	 * @var array
	 *
	 * @see EntityFieldQuery::entityCondition()
	 */
	public $entityConditions = array();

	/**
	 * List of field conditions.
	 *
	 * @var array
	 *
	 * @see EntityFieldQuery::fieldCondition()
	 */
	public $fieldConditions = array();

	/**
	 * List of field meta conditions (language and delta).
	 *
	 * Field conditions operate on columns specified by hook_field_schema(),
	 * the meta conditions operate on columns added by the system: delta
	 * and language. These can not be mixed with the field conditions because
	 * field columns can have any name including delta and language.
	 *
	 * @var array
	 *
	 * @see EntityFieldQuery::fieldLanguageCondition()
	 * @see EntityFieldQuery::fielDeltaCondition()
	 */
	public $fieldMetaConditions = array();

	/**
	 * List of property conditions.
	 *
	 * @var array
	 *
	 * @see EntityFieldQuery::propertyCondition()
	 */
	public $propertyConditions = array();

	/**
	 * List of order clauses.
	 *
	 * @var array
	 */
	public $order = array();

	/**
	 * The query range.
	 *
	 * @var array
	 *
	 * @see EntityFieldQuery::range()
	 */
	public $range = array();

	/**
	 * The query pager data.
	 *
	 * @var array
	 *
	 * @see EntityFieldQuery::pager()
	 */
	public $pager = array();

	/**
	 * Query behavior for deleted data.
	 *
	 * TRUE to return only deleted data, FALSE to return only non-deleted data,
	 * EntityFieldQuery::RETURN_ALL to return everything.
	 *
	 * @see EntityFieldQuery::deleted()
	 */
	public $deleted = FALSE;

	/**
	 * A list of field arrays used.
	 *
	 * Field names passed to EntityFieldQuery::fieldCondition() and
	 * EntityFieldQuery::fieldOrderBy() are run through field_info_field() before
	 * stored in this array. This way, the elements of this array are field
	 * arrays.
	 *
	 * @var array
	 */
	public $fields = array();

	/**
	 * TRUE if this is a count query, FALSE if it isn't.
	 *
	 * @var boolean
	 */
	public $count = FALSE;

	/**
	 * Flag indicating whether this is querying current or all revisions.
	 *
	 * @var int
	 *
	 * @see EntityFieldQuery::age()
	 */
	public $age = FIELD_LOAD_CURRENT;

	/**
	 * A list of the tags added to this query.
	 *
	 * @var array
	 *
	 * @see EntityFieldQuery::addTag()
	 */
	public $tags = array();

	/**
	 * A list of metadata added to this query.
	 *
	 * @var array
	 *
	 * @see EntityFieldQuery::addMetaData()
	 */
	public $metaData = array();

	/**
	 * The ordered results.
	 *
	 * @var array
	 *
	 * @see EntityFieldQuery::execute().
	 */
	public $orderedResults = array();

	/**
	 * The method executing the query, if it is overriding the default.
	 *
	 * @var string
	 *
	 * @see EntityFieldQuery::execute().
	 */
	public $executeCallback = '';

	/**
	 * Adds a condition on entity-generic metadata.
	 *
	 * If the overall query contains only entity conditions or ordering, or if
	 * there are property conditions, then specifying the entity type is
	 * mandatory. If there are field conditions or ordering but no property
	 * conditions or ordering, then specifying an entity type is optional. While
	 * the field storage engine might support field conditions on more than one
	 * entity type, there is no way to query across multiple entity base tables by
	 * default. To specify the entity type, pass in 'entity_type' for $name,
	 * the type as a string for $value, and no $operator (it's disregarded).
	 *
	 * 'bundle', 'revision_id' and 'entity_id' have no such restrictions.
	 *
	 * Note: The "comment" and "taxonomy_term" entity types don't support bundle
	 * conditions. For "taxonomy_term", propertyCondition('vid') can be used
	 * instead.
	 *
	 * @param $name
	 *   'entity_type', 'bundle', 'revision_id' or 'entity_id'.
	 * @param $value
	 *   The value for $name. In most cases, this is a scalar. For more complex
	 *   options, it is an array. The meaning of each element in the array is
	 *   dependent on $operator.
	 * @param $operator
	 *   Possible values:
	 *   - '=', '<>', '>', '>=', '<', '<=', 'STARTS_WITH', 'CONTAINS': These
	 *     operators expect $value to be a literal of the same type as the
	 *     column.
	 *   - 'IN', 'NOT IN': These operators expect $value to be an array of
	 *     literals of the same type as the column.
	 *   - 'BETWEEN': This operator expects $value to be an array of two literals
	 *     of the same type as the column.
	 *   The operator can be omitted, and will default to 'IN' if the value is an
	 *   array, or to '=' otherwise.
	 *
	 * @return EntityFieldQuery
	 *   The called object.
	 */
	public function entityCondition($name, $value, $operator = NULL) {
		// The '!=' operator is deprecated in favour of the '<>' operator since the
		// latter is ANSI SQL compatible.
		if ($operator == '!=') {
			$operator = '<>';
		}
		$this->entityConditions[$name] = array(
				'value' => $value,
				'operator' => $operator,
		);
		return $this;
	}

	/**
	 * Adds a condition on field values.
	 *
	 * @param $field
	 *   Either a field name or a field array.
	 * @param $column
	 *   The column that should hold the value to be matched.
	 * @param $value
	 *   The value to test the column value against.
	 * @param $operator
	 *   The operator to be used to test the given value.
	 * @param $delta_group
	 *   An arbitrary identifier: conditions in the same group must have the same
	 *   $delta_group.
	 * @param $language_group
	 *   An arbitrary identifier: conditions in the same group must have the same
	 *   $language_group.
	 *
	 * @return EntityFieldQuery
	 *   The called object.
	 *
	 * @see EntityFieldQuery::addFieldCondition
	 * @see EntityFieldQuery::deleted
	 */
	public function fieldCondition($field, $column = NULL, $value = NULL, $operator = NULL, $delta_group = NULL, $language_group = NULL) {
		return $this->addFieldCondition($this->fieldConditions, $field, $column, $value, $operator, $delta_group, $language_group);
	}

	/**
	 * Adds a condition on the field language column.
	 *
	 * @param $field
	 *   Either a field name or a field array.
	 * @param $value
	 *   The value to test the column value against.
	 * @param $operator
	 *   The operator to be used to test the given value.
	 * @param $delta_group
	 *   An arbitrary identifier: conditions in the same group must have the same
	 *   $delta_group.
	 * @param $language_group
	 *   An arbitrary identifier: conditions in the same group must have the same
	 *   $language_group.
	 *
	 * @return EntityFieldQuery
	 *   The called object.
	 *
	 * @see EntityFieldQuery::addFieldCondition
	 * @see EntityFieldQuery::deleted
	 */
	public function fieldLanguageCondition($field, $value = NULL, $operator = NULL, $delta_group = NULL, $language_group = NULL) {
		return $this->addFieldCondition($this->fieldMetaConditions, $field, 'language', $value, $operator, $delta_group, $language_group);
	}

	/**
	 * Adds a condition on the field delta column.
	 *
	 * @param $field
	 *   Either a field name or a field array.
	 * @param $value
	 *   The value to test the column value against.
	 * @param $operator
	 *   The operator to be used to test the given value.
	 * @param $delta_group
	 *   An arbitrary identifier: conditions in the same group must have the same
	 *   $delta_group.
	 * @param $language_group
	 *   An arbitrary identifier: conditions in the same group must have the same
	 *   $language_group.
	 *
	 * @return EntityFieldQuery
	 *   The called object.
	 *
	 * @see EntityFieldQuery::addFieldCondition
	 * @see EntityFieldQuery::deleted
	 */
	public function fieldDeltaCondition($field, $value = NULL, $operator = NULL, $delta_group = NULL, $language_group = NULL) {
		return $this->addFieldCondition($this->fieldMetaConditions, $field, 'delta', $value, $operator, $delta_group, $language_group);
	}

	/**
	 * Adds the given condition to the proper condition array.
	 *
	 * @param $conditions
	 *   A reference to an array of conditions.
	 * @param $field
	 *   Either a field name or a field array.
	 * @param $column
	 *   A column defined in the hook_field_schema() of this field. If this is
	 *   omitted then the query will find only entities that have data in this
	 *   field, using the entity and property conditions if there are any.
	 * @param $value
	 *   The value to test the column value against. In most cases, this is a
	 *   scalar. For more complex options, it is an array. The meaning of each
	 *   element in the array is dependent on $operator.
	 * @param $operator
	 *   Possible values:
	 *   - '=', '<>', '>', '>=', '<', '<=', 'STARTS_WITH', 'CONTAINS': These
	 *     operators expect $value to be a literal of the same type as the
	 *     column.
	 *   - 'IN', 'NOT IN': These operators expect $value to be an array of
	 *     literals of the same type as the column.
	 *   - 'BETWEEN': This operator expects $value to be an array of two literals
	 *     of the same type as the column.
	 *   The operator can be omitted, and will default to 'IN' if the value is an
	 *   array, or to '=' otherwise.
	 * @param $delta_group
	 *   An arbitrary identifier: conditions in the same group must have the same
	 *   $delta_group. For example, let's presume a multivalue field which has
	 *   two columns, 'color' and 'shape', and for entity id 1, there are two
	 *   values: red/square and blue/circle. Entity ID 1 does not have values
	 *   corresponding to 'red circle', however if you pass 'red' and 'circle' as
	 *   conditions, it will appear in the  results - by default queries will run
	 *   against any combination of deltas. By passing the conditions with the
	 *   same $delta_group it will ensure that only values attached to the same
	 *   delta are matched, and entity 1 would then be excluded from the results.
	 * @param $language_group
	 *   An arbitrary identifier: conditions in the same group must have the same
	 *   $language_group.
	 *
	 * @return EntityFieldQuery
	 *   The called object.
	 */
	protected function addFieldCondition(&$conditions, $field, $column = NULL, $value = NULL, $operator = NULL, $delta_group = NULL, $language_group = NULL) {
		// The '!=' operator is deprecated in favour of the '<>' operator since the
		// latter is ANSI SQL compatible.
		if ($operator == '!=') {
			$operator = '<>';
		}
		if (is_scalar($field)) {
			$field_definition = field_info_field($field);
			if (empty($field_definition)) {
				throw new EntityFieldQueryException(t('Unknown field: @field_name', array('@field_name' => $field)));
			}
			$field = $field_definition;
		}
		// Ensure the same index is used for field conditions as for fields.
		$index = count($this->fields);
		$this->fields[$index] = $field;
		if (isset($column)) {
			$conditions[$index] = array(
					'field' => $field,
					'column' => $column,
					'value' => $value,
					'operator' => $operator,
					'delta_group' => $delta_group,
					'language_group' => $language_group,
			);
		}
		return $this;
	}

	/**
	 * Adds a condition on an entity-specific property.
	 *
	 * An $entity_type must be specified by calling
	 * EntityFieldCondition::entityCondition('entity_type', $entity_type) before
	 * executing the query. Also, by default only entities stored in SQL are
	 * supported; however, EntityFieldQuery::executeCallback can be set to handle
	 * different entity storage.
	 *
	 * @param $column
	 *   A column defined in the hook_schema() of the base table of the entity.
	 * @param $value
	 *   The value to test the field against. In most cases, this is a scalar. For
	 *   more complex options, it is an array. The meaning of each element in the
	 *   array is dependent on $operator.
	 * @param $operator
	 *   Possible values:
	 *   - '=', '<>', '>', '>=', '<', '<=', 'STARTS_WITH', 'CONTAINS': These
	 *     operators expect $value to be a literal of the same type as the
	 *     column.
	 *   - 'IN', 'NOT IN': These operators expect $value to be an array of
	 *     literals of the same type as the column.
	 *   - 'BETWEEN': This operator expects $value to be an array of two literals
	 *     of the same type as the column.
	 *   The operator can be omitted, and will default to 'IN' if the value is an
	 *   array, or to '=' otherwise.
	 *
	 * @return EntityFieldQuery
	 *   The called object.
	 */
	public function propertyCondition($column, $value, $operator = NULL) {
		// The '!=' operator is deprecated in favour of the '<>' operator since the
		// latter is ANSI SQL compatible.
		if ($operator == '!=') {
			$operator = '<>';
		}
		$this->propertyConditions[] = array(
				'column' => $column,
				'value' => $value,
				'operator' => $operator,
		);
		return $this;
	}

	/**
	 * Orders the result set by entity-generic metadata.
	 *
	 * If called multiple times, the query will order by each specified column in
	 * the order this method is called.
	 *
	 * Note: The "comment" and "taxonomy_term" entity types don't support ordering
	 * by bundle. For "taxonomy_term", propertyOrderBy('vid') can be used instead.
	 *
	 * @param $name
	 *   'entity_type', 'bundle', 'revision_id' or 'entity_id'.
	 * @param $direction
	 *   The direction to sort. Legal values are "ASC" and "DESC".
	 *
	 * @return EntityFieldQuery
	 *   The called object.
	 */
	public function entityOrderBy($name, $direction = 'ASC') {
		$this->order[] = array(
				'type' => 'entity',
				'specifier' => $name,
				'direction' => $direction,
		);
		return $this;
	}

	/**
	 * Orders the result set by a given field column.
	 *
	 * If called multiple times, the query will order by each specified column in
	 * the order this method is called.
	 *
	 * @param $field
	 *   Either a field name or a field array.
	 * @param $column
	 *   A column defined in the hook_field_schema() of this field. entity_id and
	 *   bundle can also be used.
	 * @param $direction
	 *   The direction to sort. Legal values are "ASC" and "DESC".
	 *
	 * @return EntityFieldQuery
	 *   The called object.
	 */
	public function fieldOrderBy($field, $column, $direction = 'ASC') {
		if (is_scalar($field)) {
			$field_definition = field_info_field($field);
			if (empty($field_definition)) {
				throw new EntityFieldQueryException(t('Unknown field: @field_name', array('@field_name' => $field)));
			}
			$field = $field_definition;
		}
		// Save the index used for the new field, for later use in field storage.
		$index = count($this->fields);
		$this->fields[$index] = $field;
		$this->order[] = array(
				'type' => 'field',
				'specifier' => array(
						'field' => $field,
						'index' => $index,
						'column' => $column,
				),
				'direction' => $direction,
		);
		return $this;
	}

	/**
	 * Orders the result set by an entity-specific property.
	 *
	 * An $entity_type must be specified by calling
	 * EntityFieldCondition::entityCondition('entity_type', $entity_type) before
	 * executing the query.
	 *
	 * If called multiple times, the query will order by each specified column in
	 * the order this method is called.
	 *
	 * @param $column
	 *   The column on which to order.
	 * @param $direction
	 *   The direction to sort. Legal values are "ASC" and "DESC".
	 *
	 * @return EntityFieldQuery
	 *   The called object.
	 */
	public function propertyOrderBy($column, $direction = 'ASC') {
		$this->order[] = array(
				'type' => 'property',
				'specifier' => $column,
				'direction' => $direction,
		);
		return $this;
	}

	/**
	 * Sets the query to be a count query only.
	 *
	 * @return EntityFieldQuery
	 *   The called object.
	 */
	public function count() {
		$this->count = TRUE;
		return $this;
	}

	/**
	 * Restricts a query to a given range in the result set.
	 *
	 * @param $start
	 *   The first entity from the result set to return. If NULL, removes any
	 *   range directives that are set.
	 * @param $length
	 *   The number of entities to return from the result set.
	 *
	 * @return EntityFieldQuery
	 *   The called object.
	 */
	public function range($start = NULL, $length = NULL) {
		$this->range = array(
				'start' => $start,
				'length' => $length,
		);
		return $this;
	}

	/**
	 * Enable a pager for the query.
	 *
	 * @param $limit
	 *   An integer specifying the number of elements per page.  If passed a false
	 *   value (FALSE, 0, NULL), the pager is disabled.
	 * @param $element
	 *   An optional integer to distinguish between multiple pagers on one page.
	 *   If not provided, one is automatically calculated.
	 *
	 * @return EntityFieldQuery
	 *   The called object.
	 */
	public function pager($limit = 10, $element = NULL) {
		if (!isset($element)) {
			$element = PagerDefault::$maxElement++;
		}
		elseif ($element >= PagerDefault::$maxElement) {
			PagerDefault::$maxElement = $element + 1;
		}

		$this->pager = array(
				'limit' => $limit,
				'element' => $element,
		);
		return $this;
	}

	/**
	 * Enable sortable tables for this query.
	 *
	 * @param $headers
	 *   An EFQ Header array based on which the order clause is added to the query.
	 *
	 * @return EntityFieldQuery
	 *   The called object.
	 */
	public function tableSort(&$headers) {
		// If 'field' is not initialized, the header columns aren't clickable
		foreach ($headers as $key =>$header) {
			if (is_array($header) && isset($header['specifier'])) {
				$headers[$key]['field'] = '';
			}
		}

		$order = tablesort_get_order($headers);
		$direction = tablesort_get_sort($headers);
		foreach ($headers as $header) {
			if (is_array($header) && ($header['data'] == $order['name'])) {
				if ($header['type'] == 'field') {
					$this->fieldOrderBy($header['specifier']['field'], $header['specifier']['column'], $direction);
				}
				else {
					$header['direction'] = $direction;
					$this->order[] = $header;
				}
			}
		}

		return $this;
	}

	/**
	 * Filters on the data being deleted.
	 *
	 * @param $deleted
	 *   TRUE to only return deleted data, FALSE to return non-deleted data,
	 *   EntityFieldQuery::RETURN_ALL to return everything. Defaults to FALSE.
	 *
	 * @return EntityFieldQuery
	 *   The called object.
	 */
	public function deleted($deleted = TRUE) {
		$this->deleted = $deleted;
		return $this;
	}

	/**
	 * Queries the current or every revision.
	 *
	 * Note that this only affects field conditions. Property conditions always
	 * apply to the current revision.
	 * @TODO: Once revision tables have been cleaned up, revisit this.
	 *
	 * @param $age
	 *   - FIELD_LOAD_CURRENT (default): Query the most recent revisions for all
	 *     entities. The results will be keyed by entity type and entity ID.
	 *   - FIELD_LOAD_REVISION: Query all revisions. The results will be keyed by
	 *     entity type and entity revision ID.
	 *
	 * @return EntityFieldQuery
	 *   The called object.
	 */
	public function age($age) {
		$this->age = $age;
		return $this;
	}

	/**
	 * Adds a tag to the query.
	 *
	 * Tags are strings that mark a query so that hook_query_alter() and
	 * hook_query_TAG_alter() implementations may decide if they wish to alter
	 * the query. A query may have any number of tags, and they must be valid PHP
	 * identifiers (composed of letters, numbers, and underscores). For example,
	 * queries involving nodes that will be displayed for a user need to add the
	 * tag 'node_access', so that the node module can add access restrictions to
	 * the query.
	 *
	 * If an entity field query has tags, it must also have an entity type
	 * specified, because the alter hook will need the entity base table.
	 *
	 * @param string $tag
	 *   The tag to add.
	 *
	 * @return EntityFieldQuery
	 *   The called object.
	 */
	public function addTag($tag) {
		$this->tags[$tag] = $tag;
		return $this;
	}

	/**
	 * Adds additional metadata to the query.
	 *
	 * Sometimes a query may need to provide additional contextual data for the
	 * alter hook. The alter hook implementations may then use that information
	 * to decide if and how to take action.
	 *
	 * @param $key
	 *   The unique identifier for this piece of metadata. Must be a string that
	 *   follows the same rules as any other PHP identifier.
	 * @param $object
	 *   The additional data to add to the query. May be any valid PHP variable.
	 *
	 * @return EntityFieldQuery
	 *   The called object.
	 */
	public function addMetaData($key, $object) {
		$this->metaData[$key] = $object;
		return $this;
	}

	/**
	 * Executes the query.
	 *
	 * After executing the query, $this->orderedResults will contain a list of
	 * the same stub entities in the order returned by the query. This is only
	 * relevant if there are multiple entity types in the returned value and
	 * a field ordering was requested. In every other case, the returned value
	 * contains everything necessary for processing.
	 *
	 * @return
	 *   Either a number if count() was called or an array of associative
	 *   arrays of stub entities. The outer array keys are entity types, and the
	 *   inner array keys are the relevant ID. (In most this cases this will be
	 *   the entity ID. The only exception is when age=FIELD_LOAD_REVISION is used
	 *   and field conditions or sorts are present -- in this case, the key will
	 *   be the revision ID.) The inner array values are always stub entities, as
	 *   returned by entity_create_stub_entity(). To traverse the returned array:
	 *   @code
	 *     foreach ($query->execute() as $entity_type => $entities) {
	 *       foreach ($entities as $entity_id => $entity) {
	 *   @endcode
	 *   Note if the entity type is known, then the following snippet will load
	 *   the entities found:
	 *   @code
	 *     $result = $query->execute();
	 *     $entities = entity_load($my_type, array_keys($result[$my_type]));
	 *   @endcode
	 */
	public function execute() {
		// Give a chance to other modules to alter the query.
		drupal_alter('entity_query', $this);
		$this->altered = TRUE;

		// Initialize the pager.
		$this->initializePager();

		// Execute the query using the correct callback.
		$result = call_user_func($this->queryCallback(), $this);

		return $result;
	}

	/**
	 * Determines the query callback to use for this entity query.
	 *
	 * @return
	 *   A callback that can be used with call_user_func().
	 */
	public function queryCallback() {
		// Use the override from $this->executeCallback. It can be set either
		// while building the query, or using hook_entity_query_alter().
		if (function_exists($this->executeCallback)) {
			return $this->executeCallback;
		}
		// If there are no field conditions and sorts, and no execute callback
		// then we default to querying entity tables in SQL.
		if (empty($this->fields)) {
			return array($this, 'propertyQuery');
		}
		// If no override, find the storage engine to be used.
		foreach ($this->fields as $field) {
			if (!isset($storage)) {
				$storage = $field['storage']['module'];
			}
			elseif ($storage != $field['storage']['module']) {
				throw new EntityFieldQueryException(t("Can't handle more than one field storage engine"));
			}
		}
		if ($storage) {
			// Use hook_field_storage_query() from the field storage.
			return $storage . '_field_storage_query';
		}
		else {
			throw new EntityFieldQueryException(t("Field storage engine not found."));
		}
	}

	/**
	 * Queries entity tables in SQL for property conditions and sorts.
	 *
	 * This method is only used if there are no field conditions and sorts.
	 *
	 * @return
	 *   See EntityFieldQuery::execute().
	 */
	protected function propertyQuery() {
		if (empty($this->entityConditions['entity_type'])) {
			throw new EntityFieldQueryException(t('For this query an entity type must be specified.'));
		}
		$entity_type = $this->entityConditions['entity_type']['value'];
		$entity_info = entity_get_info($entity_type);
		if (empty($entity_info['base table'])) {
			throw new EntityFieldQueryException(t('Entity %entity has no base table.', array('%entity' => $entity_type)));
		}
		$base_table = $entity_info['base table'];
		$base_table_schema = drupal_get_schema($base_table);
		$select_query = db_select($base_table);
		$select_query->addExpression(':entity_type', 'entity_type', array(':entity_type' => $entity_type));
		// Process the property conditions.
		foreach ($this->propertyConditions as $property_condition) {
			$this->addCondition($select_query, "$base_table." . $property_condition['column'], $property_condition);
		}
		// Process the four possible entity condition.
		// The id field is always present in entity keys.
		$sql_field = $entity_info['entity keys']['id'];
		$id_map['entity_id'] = $sql_field;
		$select_query->addField($base_table, $sql_field, 'entity_id');
		if (isset($this->entityConditions['entity_id'])) {
			$this->addCondition($select_query, $sql_field, $this->entityConditions['entity_id']);
		}

		// If there is a revision key defined, use it.
		if (!empty($entity_info['entity keys']['revision'])) {
			$sql_field = $entity_info['entity keys']['revision'];
			$select_query->addField($base_table, $sql_field, 'revision_id');
			if (isset($this->entityConditions['revision_id'])) {
				$this->addCondition($select_query, $sql_field, $this->entityConditions['revision_id']);
			}
		}
		else {
			$sql_field = 'revision_id';
			$select_query->addExpression('NULL', 'revision_id');
		}
		$id_map['revision_id'] = $sql_field;

		// Handle bundles.
		if (!empty($entity_info['entity keys']['bundle'])) {
			$sql_field = $entity_info['entity keys']['bundle'];
			$having = FALSE;

			if (!empty($base_table_schema['fields'][$sql_field])) {
				$select_query->addField($base_table, $sql_field, 'bundle');
			}
		}
		else {
			$sql_field = 'bundle';
			$select_query->addExpression(':bundle', 'bundle', array(':bundle' => $entity_type));
			$having = TRUE;
		}
		$id_map['bundle'] = $sql_field;
		if (isset($this->entityConditions['bundle'])) {
			$this->addCondition($select_query, $sql_field, $this->entityConditions['bundle'], $having);
		}

		// Order the query.
		foreach ($this->order as $order) {
			if ($order['type'] == 'entity') {
				$key = $order['specifier'];
				if (!isset($id_map[$key])) {
					throw new EntityFieldQueryException(t('Do not know how to order on @key for @entity_type', array('@key' => $key, '@entity_type' => $entity_type)));
				}
				$select_query->orderBy($id_map[$key], $order['direction']);
			}
			elseif ($order['type'] == 'property') {
				$select_query->orderBy("$base_table." . $order['specifier'], $order['direction']);
			}
		}

		return $this->finishQuery($select_query);
	}

	/**
	 * Get the total number of results and initialize a pager for the query.
	 *
	 * This query can be detected by checking for ($this->pager && $this->count),
	 * which allows a driver to return 0 from the count query and disable
	 * the pager.
	 */
	function initializePager() {
		if ($this->pager && !$this->count) {
			$page = pager_find_page($this->pager['element']);
			$count_query = clone $this;
			$this->pager['total'] = $count_query->count()->execute();
			$this->pager['start'] = $page * $this->pager['limit'];
			pager_default_initialize($this->pager['total'], $this->pager['limit'], $this->pager['element']);
			$this->range($this->pager['start'], $this->pager['limit']);
		}
	}

	/**
	 * Finishes the query.
	 *
	 * Adds tags, metaData, range and returns the requested list or count.
	 *
	 * @param SelectQuery $select_query
	 *   A SelectQuery which has entity_type, entity_id, revision_id and bundle
	 *   fields added.
	 * @param $id_key
	 *   Which field's values to use as the returned array keys.
	 *
	 * @return
	 *   See EntityFieldQuery::execute().
	 */
	function finishQuery($select_query, $id_key = 'entity_id') {
		foreach ($this->tags as $tag) {
			$select_query->addTag($tag);
		}
		foreach ($this->metaData as $key => $object) {
			$select_query->addMetaData($key, $object);
		}
		$select_query->addMetaData('entity_field_query', $this);
		if ($this->range) {
			$select_query->range($this->range['start'], $this->range['length']);
		}
		if ($this->count) {
			return $select_query->countQuery()->execute()->fetchField();
		}
		$return = array();
		foreach ($select_query->execute() as $partial_entity) {
			$bundle = isset($partial_entity->bundle) ? $partial_entity->bundle : NULL;
			$entity = entity_create_stub_entity($partial_entity->entity_type, array($partial_entity->entity_id, $partial_entity->revision_id, $bundle));
			$return[$partial_entity->entity_type][$partial_entity->$id_key] = $entity;
			$this->ordered_results[] = $partial_entity;
		}
		return $return;
	}

	/**
	 * Adds a condition to an already built SelectQuery (internal function).
	 *
	 * This is a helper for hook_entity_query() and hook_field_storage_query().
	 *
	 * @param SelectQuery $select_query
	 *   A SelectQuery object.
	 * @param $sql_field
	 *   The name of the field.
	 * @param $condition
	 *   A condition as described in EntityFieldQuery::fieldCondition() and
	 *   EntityFieldQuery::entityCondition().
	 * @param $having
	 *   HAVING or WHERE. This is necessary because SQL can't handle WHERE
	 *   conditions on aliased columns.
	 */
	public function addCondition(SelectQuery $select_query, $sql_field, $condition, $having = FALSE) {
		$method = $having ? 'havingCondition' : 'condition';
		$like_prefix = '';
		switch ($condition['operator']) {
			case 'CONTAINS':
				$like_prefix = '%';
			case 'STARTS_WITH':
				$select_query->$method($sql_field, $like_prefix . db_like($condition['value']) . '%', 'LIKE');
				break;
			default:
				$select_query->$method($sql_field, $condition['value'], $condition['operator']);
		}
	}

}

/**
 * Exception thrown when a malformed entity is passed.
 */
class EntityMalformedException extends Exception { }
